The present invention relates to color filter arrays for solid-state image devices or liquid crystal display devices, and to a method for producing the same.
As a color filter array formed on a device such as a solid-state image device or a liquid crystal display device, there has been known a color filter array (2) constituted of a red filter layer (R), a green filter layer (G), and a blue filter layer (B) formed so as to be adjoining to each other in the same plane of a substrate (1) (FIG. 1). In the color filter array (2), the filter layers (R), (G), (B) are arranged in a striped pattern (FIG. 2) or a lattice-like pattern (mosaic) (FIG. 3).
A variety of processes for producing such color filter array have been proposed. Among them, so-called “color resist method” is in wide practical use. In the color resist method, the patterning is effected by exposing a photosensitive resin composition comprising colorants to light and developing, and the patterning is repeated in sequence in the required times.
As the photosensitive resin composition which is employed in the color resist method, those employing pigments as colorants are in wide use. However, such pigments are not suitable for the formation of fine or minute patterns, for they are granular and do not dissolve in developers, and developing residue is generated.
As a photosensitive resin composition for obtaining a finely patterned color filter array, a photosensitive resin composition employing dyes as colorants has also been known. For example, Japanese Patent Application Laid-Open No. 6-75375 discloses a negative photosensitive resin composition comprising dyes, and Japanese Patent Publication No. 7-111485 discloses a positive photosensitive resin composition comprising 10 to 50%, on a dry weight basis, of a dye soluble in the solvent used in the positive photosensitive resin composition. (Hereinafter, “JP-A-” is used for indicating Japanese Patent Application Laid-Open, and “JP-B-” is used for indicating Japanese Patent Publication.)
Colorants comprised in photosensitive resin compositions used for producing color filter arrays, such as those described above, are required to have the following two properties.
(1) Good spectroscopic characteristics, that is, showing sufficient absorption within the predetermined visible ray region and no unnecessary absorption in the other region.
(2) Good light fastness, that is, no burn-in due to the decolorization of dyes under normal operating conditions
However, none of the dyes employed in conventional photosensitive resin compositions has both of the above-described two properties.
For example, although the green filter layer of a color filter is desired to have a small transmittance at a wavelength of 450 nm and large transmittance at a wavelength of 535 nm, in the conventional photosensitive resin compositions, attempts to lower the transmittance at 450 nm cause a decrease in transmittance at 535 nm, deteriorating the spectroscopic characteristics. The attempts also cause decrease in transmittance at a wavelength of from 350 to 400 nm. As a result, the amount of exposure energy required for the patterning is raised, causing a reduction in the productivity of color filters.
Such problems of conventional photosensitive resin compositions will be mentioned below more concretely.
A photosensitive resin composition comprising a copper phthalocyanine dye and a pirazolone azo dye (C.I. Solvent Yellow 88) is described in above-mentioned JP-B-7-111485. Both dyes are excellent in light fastness. However, since C.I. Solvent Yellow 88 (pirazolone azo dye) has relatively high absorptivity of near-ultraviolet ray employed for the exposure, the amount of the dye in the composition is limited, and the transmittance of the resulting green filter layer at 450 nm tends to become large. In addition, since the dyes do not have sufficient high transmittance at 535 nm, transmittance with respect to green light of the resulting green filter layer tends to decrease. As a result, color filters having a green filter layer formed by using such photosensitive resin composition were not always satisfactory in their performance. As a matter of fact, according to the gazette, the transmittance of a 2 μm-thick green filter layer formed by using such photosensitive resin composition is 6% at 450 nm, 56% at 535 nm, and 4% at 650 nm.
A colorant having good spectroscopic characteristics is known. However, none of colorants having good spectroscopic characteristics is satisfactory in light fastness. Therefore, it has been difficult to manufacture a color filter array having a practical green filter layer.
The inventors of the present invention have made intensive and extensive studies to develop a color filter array having a green filter layer having good spectroscopic characteristics as well as good light fastness. As a result, they have found that the use of at least two types of specific dyes realizes the formation of a green filter layer satisfactory both in spectroscopic properties and light fastness. The present invention was accomplished based on this finding.